Oxidation-reduction or redox reactions take place in electrochemical cells. There are two types of electrochemical cells. Spontaneous reactions occur in galvanic (voltaic) cells; nonspontaneous reactions occur in electrolytic cells. Both types of cells contain electrodes where the oxidation and reduction reactions occur. Oxidation occurs at the electrode termed the anode and reduction occurs at the electrode called the cathode.
The anode of a galvanic cell is negatively charged, since the spontaneous oxidation at the anode is the source of the cell's electrons or negative charge. The cathode of a galvanic cell is its positive terminal.
Devices for electrochemical cells comprising galvanic couples are known in the art e.g. US 2011/0118655 A1 discloses a device for treatment of skin comprising a substrate comprising a plurality of discrete galvanic couples, each galvanic couple comprising a first conductive electrode that is an anode in electronic communication with a second conductive electrode that is a cathode.
Devices with power sources, such as batteries are also known in the art. US 2010/0057147 A1 discloses a device comprising a first electrode, a second electrode and a power delivery unit in electrical communication with the electrodes, the power delivery unit providing a customised dose of electricity to a treatment area.
In both galvanic and electrolytic cells, oxidation takes place at the anode and electrons flow from the anode to the cathode.
WO 2007/147947 discloses a thin film structure comprising a substrate with a thin conductive layer containing an oxidising enzyme mixed with an electron transfer mediator. The thin layer is protected against wetting to allow for its storage in dry conditions and further being sufficiently porous to allow for immediate activation of the oxidizing enzyme when contacted with an aqueous solution.
WO 2013/130145 discloses methods, systems, and devices for implementing a biofuel cell device for extracting energy from a biofuel. In one aspect, a biofuel cell device includes a substrate, an anode including a catalyst to facilitate the conversion of a fuel in a biological fluid in an oxidative process that releases electrons captured at the anode, thereby extracting energy from the fuel substance, a cathode configured on the substrate adjacent to the anode and separated from the anode by a spacing region, and a load electrically coupled to the anode and cathode via electrical interconnects to obtain the extracted energy as electrical energy.
U.S. Pat. No. 8,758,936 discloses a thin film structure, method of producing it and the use thereof. The thin film structure comprises a substrate with a thin conductive layer containing an oxidizing enzyme mixed with an electron transfer mediator. The thin layer is protected against wetting to allow for its storage in dry conditions and further being sufficiently porous to allow for immediate activation of the oxidizing enzyme when contacted with an aqueous solution. The thin film can be used as a cathode in electrochemical fuel cells.
WO 2005/079913 A1 and WO 2014/178943 A1 disclose apparatuses including multiple first reservoirs and multiple second reservoirs joined with a substrate. Selected ones of the first reservoirs include a reducing agent, and first reservoir surfaces of selected ones of the first reservoirs are proximate to a first substrate surface. Selected ones of the second reservoirs include an oxidizing agent, and second reservoir surfaces of selected ones of the second reservoirs are proximate to the first substrate surface. The device is intended for directing the migration of cells and comprises biocompatible electrodes capable of generating a low level electric field or low level micro current when contacted with an electrolytic solution.